Third generation and more recent radiotelephony systems already handle or will handle many services and applications requiring very high-speed data transmissions. Resources allocated to data transfers (for example files containing sound, and/or fixed or animated images), particularly through the Internet or similar networks, will account for an overwhelming part of the available resource and will probably eventually exceed resources allocated to voice communications which should remain approximately constant.
However, the total throughput available to radiotelephony equipment users is limited by the number of available frequencies. One particular method traditionally used to enable sufficient availability of resources is to increase the density of cells in a given territory. The result is thus a network infrastructure divided into “micro-cells” that are relatively small cells. One disadvantage of such a technique is that it requires a large number of fixed stations (base station (BS)), that are relatively complex and expensive elements. Furthermore, although the possible data throughput is high, it is not optimum. Furthermore, at a higher level, it is clear that management becomes more complex as the number of cells, and therefore the number of stations becomes larger.
The capacity of third generation UMTS (Universal Mobile Telecommunication System) networks is also limited by interference between adjacent cells or networks. Thus, base stations use a transmission power control making use of indications issued by a reception equipment, to avoid excessive interference.
Moreover, like all existing radiotelephony systems, third generation systems currently under development are based on an asymmetric structure. Thus, the UMTS standard defined by the 3GPP (Third generation Partnership Project) uses a symmetric distribution for the FDD (Frequency Division Duplex) main link, between the downlink channel (base station to terminal) and the uplink channel (terminal to base station). There is also a TDD (Time Division Duplex) link enabling some asymmetry. However, the asymmetry thus available is limited considering the needs of users for Internet type high-speed services, with or without mobility, on the downlink channel.
One solution then consists of using multi-carrier modulations with the W-CDMA (Wide-Code Division Multiple Access). For example, an OFDM (Orthogonal Frequency Division Multiplexing) downlink channel could be introduced, with a high speed (as described particularly in patent FR-98 04883 filed on Apr. 10 1998 by the Wavecom Company) or a UMTS network could be combined with existing or future high-speed wireless LANs (WLAN—Wireless Local Area Network) (particularly according to the ETSI HiperLAN/2 or IEEE 802.11 standards).
As for a system using CDMA, the same frequency may be used more than once for a system based on an OFDM modulation. Thus, if two adjacent cells use the same frequency (particularly when a resource is available in limited frequency), there would be interference between cells; thus, a terminal located in one cell at a frequency f1 will be disturbed by signals transmitted on an adjacent cell at the same frequency f1. The terminal will then receive delayed OFDM signals originating from two base stations. Orthogonality between OFDM sub-carriers is then no longer guaranteed, the terminal will no longer be capable of correctly demodulating the information to be sent to it.
In HiperLAN/2 type high-speed wireless networks (which particularly use an OFDM type modulation), there are more than twenty channels, so that a dynamic frequency allocation mechanism can be used to avoid having adjacent cells with the same frequency. However, this technique has the disadvantage that it is relatively complex to implement.
The invention and its various aspects are intended particularly to overcome the disadvantages of prior art.
More precisely, a first purpose of the invention is to optimise data transmission particularly by enabling a global increase in speed in one or several networks covering the same geographic area or adjacent areas.
A second purpose of the invention is to optimise data transfer from a terminal to a base station that does not necessarily have an uplink channel.